Rotation position detecting device

ABSTRACT

A rotation position detecting device includes an angular signal generator which generates pulses the cycle period of which is even or equal when a rotating object rotates at a constant rotation speed and a non-pulse portion which corresponds to a reference position, an up-down command circuit for generating an up-down command signal the frequency of which is divided to a half of the frequency of the angular signal, a pair of first counters for counting up or down the clock signal when the up-down command signal changes from a first level to a second level to reset and subsequently counting down the clock signal when the up-down command signal changes from the second level to the first level, a pair of processing circuits for providing a first and second reference values, a pair of counters which generates detection signals when the counted number of the counters becomes smaller than the first or the second reference value.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from JapanesePatent Application 2004-31944, filed Feb. 9, 2004, the contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rotation position detecting devicethat detects a reference position of a rotating object by means of arotation signal generated in synchronism with rotation of the rotatingobject.

2. Description of the Related Art

U.S. Pat. No. 5,264,844 (or its one of basic Japanese patentapplications JP-A-Hei 5-66105) discloses a rotation position detectingdevice that counts the number of clock signals to calculate the cycletime of the pulses of a rotation angle signal. Such a rotation detectingdevice includes an up-down counter and a f/K frequency dividing circuit,in which a ⅓ frequency dividing circuit and a ½ frequency dividingcircuit are combined to provide a down-clock. The above-stated rotationposition detecting device measures the cycle time of pulses by countingthe number of clock signals, from which the down-clock counts down. Thereference position can be detected when a borrow signal appears. U.S.Pat. No. 5,264,844 (or its another basic Japanese patent applicationJP-A-Hei 5-71909) also discloses a rotation position detecting device asshown in FIGS. 10, 11, 12A and 12B. In this rotation position detectingdevice 1, a frequency dividing circuit 4 divides an angle signal NE thatis sent from a rotation sensor 2 via a wave-shaping circuit 3 into ahalf to provide a pair of up-down command signals SUD1 and SUD2. A pairof up-down counters 5 and 6 counts up or counts down alternatelyaccording to the up-down command signals SUD 1 and SUD2 at each cycletime of the angle signal NE.

The direction of counting up or down by the up-down counter 5 isopposite to the direction of counting up or down by the up-down counter6. Each up-down counter counts up according to an up-clock signal CLKUthat is provided by a clock circuit 7 and counts down according to adown-clock signal CLKD that is provided by a 1/K frequency dividingcircuit 8. The clock signals applied to the up-down counters 5, 6 arecontrolled by selectors 9, 10. When edge detecting circuits 11, 12respectively detect an up-edge of the up-down command signals SUD1,SUD2, the counted values of the up-down counters 5, 6 are reset to 0.

When the rotation sensor 2 detects a non-tooth portion (in an unevencycle time), the count number of one of the up-down counters 5, 6becomes 0, so that a borrow signal or detection signal BO is outputted.Because there are two states of the down clock signals CLKD when theup-down command signals changes, the timing of transition from theup-count to the down-count may shift, so that the detection signal BOmay not be provided at a right timing, as shown in FIGS. 12A-12E and13A-13D.

Because the down clock signal CLKD is formed by dividing the up clocksignal CLKU into 1/K according to the number of non-toothed portions,the frequency of the down clock signal CLKD becomes lower than the upclock signal CLKU. Therefore, a half-cycle shift of the down clocksignal CLKD becomes K times as long as a half cycle of the up clocksignal CLKU. If the shift of the detection signal BO becomes larger, thefrequency of the clock signal has to be increased, resulting inincreasing power of the clock circuit.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved rotationposition detecting device that can accurately measure a non-pulseportion of an angular signal.

According to a first main feature of the invention, a rotation positiondetecting device includes a first counter for counting up a clock signalan up-down command signal changes from a first level to a second levelto reset and subsequently counting down the clock signal when theup-down command signal changes from the second level to the first level,a second counter for counting up the clock signal when the up-downcommand signal changes from the second level to the first level to resetand subsequently counting down the clock signal when the up-down commandsignal changes from the first level to the second level, a firstprocessing circuit for providing a first reference value P1 that isprovided by subtracting a product N1×K of the counted value N1 of thefirst counter when the up-down command signal changes from the secondlevel to the first level and a constant K that is a value larger than 1and corresponds to the non-pulse portion from a counted value N1 countedby the first counter, a second processing circuit for providing a secondreference value P2 that is provided by subtracting a product of thecounted value N2 of the second counter when the up-down command signalchanges from the first level to the second level and the constant K froma counted value N2 counted by the second counter, a first comparator forgenerating a first detection signal when the counted number N1 of thefirst counter becomes smaller than the first reference value P1 and asecond comparator for generating a second detection signal when thecounted number N2 of the second counter becomes smaller than the secondreference value P2.

In the above rotation position detecting device, the counters count upor down clock pulses of a common clock. Therefore, shift in the firstand second detection signals is limited within one cycle of the clocksignal, so that accuracy of the detection signal can be improved.Because the constant K is larger than 1, a sufficient time (within oneclock cycle) for the processing circuits to calculate can be provideduntil the counted value is counted down to an initial value (zero).Therefore, the processing circuits can be provided in either hardware orsoftware.

According to a second main feature of the invention, a rotation positiondetecting device includes substantially the same components as theabove. In this device, a first processing circuit provides a firstreference value P1 that is a product of the counted value (N2) of thesecond counter when the up-down command signal changes from the firstlevel to the second level and a constant K that corresponds to thenon-pulse portion, a second processing circuit for providing a secondreference value P2 that is a product of the counted value (N1) of thefirst counter when the up-down command signal changes from the secondlevel to the first level and the constant K. This device is also aseffective as the above device.

According to a feature in addition to the first and second features, therotation position detecting device includes a first latch circuit forlatching the counted value of the first counter when the up-down commandsignal changes from the second level to the first level and a secondlatch circuit for latching the counted value of the second counter whenthe up-down command signal changes from the first level to the secondlevel.

According to another feature in addition to the above features, therotation position detecting device further includes means for detectingone of up-edge and down edge of the angular signal in synchronism withthe clock pulse and generating a first edge signal when an edge isdetected while the up-down command signal is in the first level and asecond edge signal when an edge is detected while the up-down commandsignal is in the second level. In this feature the following operationsare carried out: the first counter is reset by the second edge signal;the second counter is reset by the first edge signal; the first latchcircuit latches the counted value of the first counter by the first edgesignal; and the second latch circuit latches the counted value of thesecond counter by the second edge signal.

According to a third main feature of the invention, a rotation positiondetecting device includes means for generating an angular signal havingpulses the cycle period of which is even or equal when a rotating objectrotates at a constant rotation speed and a non-pulse portion whichcorresponds to a reference position, a clock pulse generating circuitwhich generates pulses at equal intervals, a counter for counting thepulses of the clock signal from a reset value when the angular signalchanges from a first level to a second level, a processing circuit forproviding a reference value P by multiplying a counted value N of thecounter when the angular signal changes from the first level to thesecond level and a constant K that corresponds to the non-pulse portionand means for generating a detection signal when the counted number ofthe counter becomes larger than the reference value.

This feature also brings about similar effects as described with respectto the first and the second features.

According to a feature in addition to the third main feature, therotation position detecting device of the third main feature furtherincludes a latch circuit for latching the counted value of the counterwhen the angular signal changes from the first level to the secondlevel.

According to a feature in addition to the third main feature, therotation position detecting device of the third main feature furtherincludes a gate circuit which masks the detection signal outputted bythe comparator as long as the processing circuit is calculating thereference value.

According to a feature in addition to the third main feature, theangular signal of the rotation position detecting device of the thirdmain feature synchronizes with rotation of an internal combustionengine.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and characteristics of the present invention aswell as the functions of related parts of the present invention willbecome clear from a study of the following detailed description, theappended claims and the drawings. In the drawings:

FIG. 1 is a block diagram illustrating an electrical structure of arotation position detecting device according to the first embodiment ofthe invention;

FIGS. 2A-2R show wave shapes that respectively appear at variousportions of the electrical structure illustrated in FIG. 1;

FIGS. 3A-3D show the wave shapes shown in FIGS. 2A, 2F, 2N and 2R for alonger period of time;

FIG. 4 is a block diagram illustrating an electric structure of arotation position detecting device according to the second embodiment ofthe invention;

FIGS. 5A-5R show wave shapes that respectively appear at variousportions of the electrical structure illustrated in FIG. 4;

FIGS. 6A-6D show the wave shapes shown in FIGS. 5A, 5F, 5N and 5R for alonger period of time;

FIG. 7 is a block diagram illustrating an electric structure of arotation position detecting device according to the third embodiment ofthe invention;

FIGS. 8A-8G show wave shapes respectively appear at various portions ofthe electrical structure illustrated in FIG. 7;

FIGS. 9A-9C show the wave shapes shown in FIGS. 8A, 8D and 8G for alonger period of time;

FIG. 10 is a block diagram illustrating an electric structure of a priorart rotation position detecting device;

FIGS. 11A-11D show wave shapes respectively appear at various portionsof the electrical structure illustrated in FIG. 10;

FIGS. 12A-12E show a relationship in timing between a detection signaland an up-down command signal provided in the electrical structureillustrated in FIG. 10; and

FIGS. 13A-13D show a relationship in timing between a detection signaland an up-down command signal provided in the electrical structureillustrated in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A rotation position detecting device 21 according to the firstembodiment of the invention will be described with reference to FIGS.1-3.

As shown in FIG. 1, the rotation position detecting device 21 includesan angular signal generating unit 22, a wave shaping circuit 26, afrequency dividing circuit 27, a clock signal generating circuit orclock 28, an edge signal generating circuit 29, a pair of counters 36,37, a apir of latch circuits 38, 39, a pair of processing circuits 40,41, a constant value holding circuit 42, comparators 43, 44, AND gates45, 46 and an OR gate 47.

The rotation position detecting device 21 detects a reference positionfrom a signal NE that is sent from the angular signal generating unit22. The angular signal generating unit 22 generates an angular signalthat corresponds to a rotation position of a crank or cam shaft 23,which is an object to be detected. The angular signal generating unit 22includes a rotor 24 that has thirty four teeth 24 a on its outerperiphery at 10-degree-angle intervals, a rotation sensor 25 that ismade up of such as an electromagnetic pick-up sensor, a hall element ora photo sensor and a wave shaping circuit 26. The rotor 24 is fixed tothe crank or cam shaft 24. The above-stated non-tooth portion 24 b hastwo tooth-pitches formed between the teeth 24 a on the outer peripheryof the rotor 24. The rotation sensor 25 is disposed at a portion thatconfronts the teeth 24 a and the non-tooth portion 24 a.

The output signal of the rotation sensor 25 is sent to the wave shapingcircuit 26 to provide the angular signal NE. The output terminal of thewave shaping circuit 26 is connected to a frequency dividing circuit 27,which is composed of a D flip flop circuit whose Q terminal and Dterminal are connected. The frequency dividing circuit 27 divides thefrequency of the angular signal into a half to provide an up-downcommand signal SUD. The clock 28 provides a clock signal CLK having aconstant cycle period.

The edge signal generating circuit 29 detects each up-edge of theangular signal NE and provides edge signals SE1-SE4 based on selectedup-edges. The edge signal generating circuit 29 includes an edgedetecting circuit 30 and AND gates 31-34. The edge detecting circuit 30detects up-edges of the angular signal SE in synchronism with the clocksignal CLK to provide an edge signal SEG0 whose level transitorilybecomes H.

The AND gate 31 has input terminals for the up-down command signal SUDand the edge signal SEG0 and provides an edge signal SE1 that is thelogical product of the two signals. The edge signal SE 1 becomes a latchsignal for the latch circuit 38. The AND gate 32 has input terminals forthe up-down command signal SUD and the edge signal SEG0 and provides anedge signal SE2 that is the logical product of the two signals. The edgesignal SE2 becomes a reset signal or an initializing signal for thecounter 36. The AND gate 33 has input terminals for the up-down commandsignal SUD and the edge signal SEG0 and provides an edge signal SE3 thatis the logical product of the two signals. The edge signal SE 3 becomesa latch signal for the latch circuit 39.

The AND gate 34 has input terminals for the inversed signal of theup-down command signal SUD inversed by an inverter 35 and the edgesignal SEG0 and provides an edge signal SE4 that is the logical productof the two signals. The edge signal SE4 becomes a reset signal or aninitializing signal for the counter 37. The edge signals SE1, SE4 becomeH level when the up-down command signal SUD changes from H level to Llevel, while the edge signals SE2, SE4 become H level when the up-downcommand signal SUD changes from L level to H level.

The counters 36, 37 respectively have an up-down command terminal U/DBand a clock terminal CK. When the up-down command terminal U/DB of thecounters 36, 37 becomes L level, the counters 36, 37 count down theclock signal CLK that is inputted to the respective terminals CK. Whenthe up-down command terminal U/DB of the counters 36, 37 becomes Hlevel, the counters 36, 37 count up the clock signal CLK that isinputted to the respective terminals CK. Thus, the direction of countingby the counter 36 is always opposite to the direction of counting by thecounter 37. The counted values of the counters 36, 37 are respectivelyreset to 0 or initialized by the edge signals SE1 and SE4.

The latch circuits 38, 39 respectively latch the counted values of thecounters 36, 37 when the edge signals SE1, SE2 respectively become Hlevel. The processing circuits 40 receives the latched counted value NL1from the latch circuit 38 and a constant value K from the constant valueholding circuit 42 respectively at its input terminals to calculate areference value P1=NL1−(NL1×K) when the edge signal SE1 becomes H level.The processing circuits 40 receives the latched counted value NL2 fromthe latch circuit 39 and the same constant value K from the constantvalue holding circuit 42 respectively at its input terminals tocalculate a reference value P2=NL2−(NL2×K) when the edge signal SE3becomes H level.

Each of the processing circuits 40, 41 is composed of logical circuitsthat operate in synchronism with the clock signal CLK. The constantvalue holding circuit 42 is composed of registers and memories. Theprocessor circuit 40 provides a masking signal SM1 that keeps L levelonly for a period from time at which the edge signal SE1 changes to Hlevel until the reference value P1 has been calculated. The processorcircuit 41 provides a masking signal SM2 that keeps L level only for aperiod from time at which the edge signal SE3 changes to H level untilthe reference value P2 has been calculated.

The comparator 43 compares a counted value N1 of the counter 36 with thereference value P1 that is provided by the processing circuit 40 andprovides a detection signal SC1 when the counted value N1 is smallerthan the reference value P1. The comparator 44 also compares a countedvalue N2 of the counter 37 with the reference value P2 that is providedby the processing circuit 41 and provides a detection signal SC2 whenthe counted value N2 is smaller than the reference value P2.

The AND gate 45 has a pair of input terminals to which the detectionsignal SC1 and the masking signal SM1 are respectively inputted and anoutput terminal that outputs a masked detection signal SC1 m. The ANDgate 46 also has a pair of input terminals to which the detection signalSC2 and the masking signal SM2 are respectively inputted and an outputterminal that outputs a masked detection signal SC2 m. The OR gate 47receives the masked detection signals SC1 m, SC2 m at its inputterminals and provides a detection signal SC for the non-tooth portion24 b at its output terminal.

When the rotor 24 rotates together with the crank shaft or cam shaft 23,the rotation sensor 25 that is disposed near the rotor 24 generates asignal that changes in response to the teeth 24 a on the periphery ofthe rotor 24. This signal is formed by the wave shaping circuit 26 intothe angular signal NE that has rectangular waves. The angular signal NEis sent to the frequency dividing circuit 27 to provide the up-downcommand signal SUD. Therefore, the frequency of the up-down commandsignal SUD is a half of the angular signal NE, and the level of theup-down command signal SUD changes in synchronism with the up-edges ofthe angular signal NE.

When an up-change of the angular signal NE appears at time t1 in FIG. 2,the edge signal SE2 changes to H level, the counted value N1 of thecounter 36 is reset to 0. During the period from t1 to t3 whichcorresponds to the cycle period of the angular signal NE, the up-downcommand signal SUD keeps H level so that the counter 36 can count up theclock signal CLK.

When the next up-edge appears in the angular signal NE at time t3, theedge signal SE1 changes to H level, so that the counted value N1 of thecounter 36 is latched by the latch circuit 38. Thereafter, the up-downcommand signal SUD keeps L level during the cycle period of the angularsignal NE from t3 to t5. Therefore, the counter 36 counts down the clocksignal CLK from the latched counted value N1 (=NL1).

When the edge signal SE1 becomes H level, the processing circuit 40takes the latched count number NL1 into the input terminal thereof fromthe latch circuit 38 to calculate the reference value P1=NL1−(NL1×K)during the period from t3 to t4 (or Δt). Incidentally, arrows extendingfrom the counted value N1 to the reference value P1 in FIG. 2F indicatea functional relationship between the counted value N1 and the referencevalue P1. The processing circuit 40 keeps the reference value P1calculated last time until a new reference value P1 has been calculated.

The comparator 43 always compares the counted value N1 with thereference value P1 and provides the detection signal SC1 if the countedvalue N1 is smaller than the reference value P1. Masking by the maskingsignal SM1 is also carried out lest the detection signal is erroneouslyprovided during the above operation. In case of the non-tooth portion 24b having two tooth-pitches as shown in FIG. 1, the constant value K isset to 2.0. The reference value P1 becomes −NL1, so that N1<P1 regardingthe non-tooth portion never happens even if the rotation speed of thecrank or cam shaft 23 abruptly decreases. If the rotation speed isconstant, the edge signal SE2 becomes H level when the counted value N1decreases to 0 at time t5, as shown in FIG. 2F. In case of a constantrotation speed, the edge signal SE2 becomes H level when the countedvalue N1 is counted down to zero, and the counter 36 starts to count up.

After the counter 36 changes to count down at time t7, no H level pulseis provided in the edge signal SE2 (during the period from t9 to tlO)due to the non-tooth portion. Therefore, the counter 36 continues tocount down until the edge signal SE 2 becomes H level at time t11. As aresult, the counted value N1 becomes smaller than the reference value P1at t10, so that the detection signal SC1 becomes H level, whichindicates the non-tooth portion.

The other set of the counter 37, the latch circuit 39, the processingcircuit 41 and the comparator 44 operates in the same manner as above.When the counter 37 measures the cycle period, it can not count upduring the non-tooth period. Thus, a pair of the counters 36, 37operates to complement each other.

If the constant number K is 2.0 and the rotation speed is constant, asshown in FIGS. 3A-3D, the non-tooth portion whose tooth-pitch is largerthan 1 can be detected. In FIG. 3A, a portion indicated by A has 1.5tooth-pitches and a portion indicated by B has 2 tooth pitches.Incidentally, the constant K is determined according to the rotationspeed of the crank shaft or cam shaft 23.

Because the counters 36, 37 use the same clock signal CLK, no delay ortime shift arises when each of the counters 36, 37 changes from countingup to counting down. In other words, the shift in timing is limitedwithin one cycle period of the clock signal CLK when the edge signalsSE1-SE4 are generated by the edge signal generating circuit 29.

Second Embodiment

A rotation position detecting device according to the second embodimentof the invention will be described with reference to FIGS. 4-6.Incidentally, the same reference numeral as the precedent embodiment ofthis application indicates the same or substantially the same part,component or unit as the precedent embodiment.

As shown in FIG. 4, a rotation position detecting device 48 a pair ofprocessing circuits 40, 41 instead of the processing circuits 50, 49 ofthe rotation position detecting device 21 according to the firstembodiment. When the edge signal SE3 becomes H level, the processingcircuit 49 takes in the latched counted value NL2 from the latch circuit39 and the constant value K from the constant value holding circuit 42to calculate the reference value P2=NL2×K. When the edge signal SE1becomes H level, the processing circuit 50 takes in the latched countedvalue NL1 from the latch circuit 39 and the constant value K from theconstant value holding circuit 42 to calculate the reference valueP1=NL1×K. The processing circuits 49, 50 are composed of logicalcircuits that operate in synchronism with the clock signal CLK, andprovide masking signals SM1, SM2 during operation.

The rotation position detecting device 48 has a pair of comparators 43,44 instead of the comparator 43, 44 of the rotation position detectingdevice 21. The comparator 51 compares the counted value N1 seriallyprovided by the counter 36 with the reference value P1 provided by theprocessing circuit 49 so as to provide the detection signal SC1 if thecounted value N1 is larger than the reference value P1. The comparator52 also compares the counted value N1 serially provided by the counter37 with the reference value P2 provided by the processing circuit 50 soas to provide the detection signal SC2 if the counted value N2 is largerthan the reference value P2.

The AND gate 45 receives the detection signal SC1 and the masking signalSM1 and provides a masked detection signal SC1 m, and the AND gate 46also receives the detection signal SC2 and the masking signal SM2 andprovides a masked detection signal SC2 m. The OR gate 47 receives themasked detection signals SC1 m, SC2 m to provide a detection signal SCof the non-tooth portion 24 b.

As shown in FIG. 5, the processing circuit 50 receives a latched countedsignal NL1 from the latch circuit 38 when the edge signal SE1 becomes Hlevel at time t23 and calculates the reference value P2 that is equal toNL1×K for a period A t from t23 to t 24. The processing circuit 49 alsoreceives a latched counted signal NL2 from the latch circuit 39 when theedge signal SE2 becomes H level at time t25 and calculates the referencevalue P1 that is equal to NL2×K for the period Δ t from t25 to t 26.

The processing circuits 49, 50 keep providing the reference values P1,P2 that are calculated last time until the calculation has beencompleted. In other words, the processing circuits 49, 50 provide thenew reference values P1, P2 as soon as the calculation is completed.

The comparator 51 always compares the counted value N1 with thereference value P1 to provide the detection signal SC1 when the countedvalue N1 is larger than the reference value P1. The constant value K isset to 2 as the non-tooth portion has two tooth pitches. Therefore, thereference values P1 and P2 are respectively equal to 2×NL2 and 2×NL1, sothat N1>P1 or N2>P2 never occurs at the non-tooth portion even ifrotation speed of the crank shaft or cam shaft 23 sharply decreases. Ifthe rotation speed is constant at a time such as t23 or t25, thecounters start to count down as soon as they have counted up to NL1 orN12.

At the non-tooth portion, the edge signal SE3 does not provide a H-levelpulse (e.g. at time t29, t30) after the counter 37 is reset to count up(e.g. at time t27). Therefore, the counter 37 keeps counting up untilthe edge signal SE3 becomes H level. As a result, the counted value N2becomes larger than the reference value P2 at time t30, so that thedetection signal SC2 becomes H level to detect the non-tooth portion.

As shown in FIGS. 6A-6D, the non-tooth portion having 1.5 tooth pitches(indicated by A) as well as the non-tooth portion having 2 tooth-pitches(indicated by B) can change the detection signal from L level to H levelif the rotation speed is constant. That is, the non-tooth portion havinga tooth pitch of more than 1 can be detected if the rotation speed isconstant with the constant value K being 2.

Third Embodiment

A rotation position detecting device according to the third embodimentof the invention will be described with reference to FIGS. 7-9.

As shown in FIG. 7, the rotation position detecting device 53 includes asingle up-down counter 55, a single latch circuit 38, a singleprocessing circuit 50, a single comparator as well as an edge detectingcircuit 54 and an AND gate 45 to detect the non-tooth portion 24 b.

The edge detecting circuit 54 synchronizes with the clock signal CLK todetect up-edges of the angular signal NE and provides an edge signalSEG0 that becomes H level when each up-edge is detected. The edgedetecting circuit 54 provides an edge signal SEG1 that becomes H level alittle time after the edge signal SEG0 does. The delay time is a littlelonger than a period in which the latch circuit 38 can latch a countedvalue of the counter 55.

The counter 55 is an N-bit counter. The latch circuit 38 latches eachcounted value counted by the counter 38 by the use of the edge signalSEG0. The processing circuit 50 is formed of logical circuits thatoperate in synchronism with the clock signal CLK. The processing circuit50 receives a latched counted value NL and calculate a reference valueP=NL×K when the edge signal SEG0 becomes H level. The constant value Kis provided by a constant value holding circuit 42. The processingcircuit 50 provides a masking signal SM1 while it is calculating thereference value P.

The comparator 51 compares the counted value N with the reference valueP and provides a detection signal SC1 when the counted value N is largerthan the reference value P. The AND gate 45 receives the detectionsignal SC1 and the masking signal SM1 to provide a masked detectionsignal SC.

When an up-edge appears in the angular signal NE at time t41 as shown inFIG. 8, the edge signal SEG0 becomes H level, so that the counted numberof the counter 55 is latched by the latch circuit 38. As soon as thelatching has completed, the edge signal SEG1 becomes H level, so thatthe counted number N of the counter 55 is reset to 0.

The processing circuit 50 receives the latched counted value NL from thelatch circuit 38 to calculate the reference value P that is equal toNL×K in a period A t from t41 to t 42 each time the edge signal SEG0becomes H level.

The comparator 51 always compares the counted value N with the referencevalue P to provide the detection signal SC whenever the counted value Nis larger than the reference value P. The constant value K is set to 2as the non-tooth portion has two tooth pitches. Therefore, the referencevalue P is equal to 2×NL, so that N>P never occurs at the non-toothportion even if rotation speed of the crank shaft or cam shaft 23sharply decreases. If the rotation speed is constant at a time such ast43 or t45, the edge signal SEG1 becomes H level as soon as the countedvalue N becomes NL. Therefore, the counter 55 is reset to 0, from whereit starts to count up.

At the non-tooth portion, the edge signal SEG1 does not provide aH-level pulse (e.g. at time t49, t50) after the counter 55 is reset tocount up (e.g. at time t47). Therefore, the counter 55 keeps counting upuntil the edge signal SEG1 becomes H level (t1). As a result, thecounted value N becomes larger than the reference value P at time t50,so that the detection signal SC becomes H level to detect the non-toothportion.

As shown in FIGS. 9A-9C, the non-tooth portion having 1.5 tooth pitches(indicated by A) as well as the non-tooth portion having 2 tooth-pitches(indicated by B) can change the detection signal SC from L level to Hlevel if the rotation speed is constant. That is, the non-tooth portionhaving a tooth pitch of more than 1 can be detected if the rotationspeed is constant with the constant value K being 2.

Shift of timing is limited within a cycle period of the clock signalCLK, as the edge detecting circuit 54 provides the edge signals SEG0,SEG1 in synchronism with the clock signal CLK. The reset timing of thecounter 55 by the edge signal SEG1 delays from the edge of the angularsignal NE (edge signal SEG0) only by a holding time of the latch circuit38.

In the above embodiment, the constant value K is not limited to 2 incase that the tooth-pitch of the non-tooth portion is 2. The AND gates33 and 34 of the first and the second embodiment can be omitted becausethe edge signals SE1 and SE4 are the same and, also, the edge signalsSE2 and SE 3 are the same. The AND gates 45 and 46 can be omitted if themasking is not necessary. The latch circuits 38 and 39 can be alsoomitted if the processing circuits 40, 41, 49 and 50 includes a latchfunction.

In the foregoing description of the present invention, the invention hasbeen disclosed with reference to specific embodiments thereof. It will,however, be evident that various modifications and changes may be madeto the specific embodiments of the present invention without departingfrom the scope of the invention as set forth in the appended claims.Accordingly, the description of the present invention is to be regardedin an illustrative, rather than a restrictive, sense.

1. A rotation position detecting device comprising: means for generatingan angular signal having pulses the cycle period of which is even when arotating object rotates at a constant rotation speed and a non-pulseportion which corresponds to a reference position; a clock pulsegenerating circuit which generates pulses at equal intervals; an up-downcommand circuit for generating an up-down command signal the frequencyof which is divided to a half of the frequency of the angular signal; afirst counter for counting up the clock signal when the up-down commandsignal changes from a first level to a second level to reset andsubsequently counting down the clock signal when the up-down commandsignal changes from the second level to the first level; a secondcounter for counting up the clock signal when the up-down command signalchanges from the second level to the first level to reset andsubsequently counting down the clock signal when the up-down commandsignal changes from the first level to the second level; a firstprocessing circuit for providing a first reference value that isprovided by subtracting a product of the counted value of the firstcounter when the up-down command signal changes from the second level tothe first level and a constant that corresponds to the non-pulse portionfrom a counted value counted by the first counter; a second processingcircuit for providing a second reference value that is provided bysubtracting a product of the counted value of the second counter whenthe up-down command signal changes from the first level to the secondlevel and the constant from a counted value counted by the secondcounter; a first comparator for generating a detection signal when thecounted number of the first counter becomes smaller than the firstreference value; and a second comparator for generating a detectionsignal when the counted number of the second counter becomes smallerthan the second reference value.
 2. A rotation position detecting devicecomprising: means for generating an angular signal having pulses thecycle period of which is even when a rotating object rotates at aconstant rotation speed and a non-pulse portion which corresponds to areference position; a clock pulse generating circuit which generatesclock pulses at equal intervals; an up-down command circuit forgenerating an up-down command signal the frequency of which is dividedto a half of the frequency of the angular signal; a first counter forcounting up the clock signal when the up-down command signal changesfrom a first level to a second level to reset and subsequently countingdown the clock signal when the up-down command signal changes from thesecond level to the first level; a second counter for counting up theclock signal when the up-down command signal changes from the secondlevel to the first level to reset and subsequently counting down theclock signal when the up-down command signal changes from the firstlevel to the second level; a first processing circuit for providing afirst reference value that is a product of the counted value of thesecond counter when the up-down command signal changes from the firstlevel to the second level and the constant; a second processing circuitfor providing a second reference value that is a product of the countedvalue of the first counter when the up-down command signal changes fromthe second level to the first level and the constant; a first comparatorfor generating a detection signal when the counted number of the firstcounter becomes larger than the first reference value; and a secondcomparator for generating a detection signal when the counted number ofthe second counter becomes larger than the second reference value. 3.The rotation position detecting device as claimed in claim 1 furthercomprising: a first latch circuit for latching the counted value of thefirst counter when the up-down command signal changes from the secondlevel to the first level; and a second latch circuit for latching thecounted value of the second counter when the up-down command signalchanges from the first level to the second level.
 4. The rotationposition detecting device as claimed in claim 3, further comprisingmeans for detecting one of up-edge and down edge of the angular signalin synchronism with the clock pulse and generating a first edge signalwhen an edge is detected while the up-down command signal is in thefirst level and a second edge signal when an edge is detected while theup-down command signal is in the second level; wherein the first counteris reset by the second edge signal, the second counter is reset by thefirst edge signal, the first latch circuit latches the counted value ofthe first counter by the first edge signal, and the second latch circuitlatches the counted value of the second counter by the second edgesignal.
 5. A rotation position detecting device comprising: means forgenerating an angular signal having pulses the cycle period of which iseven when a rotating object rotates at a constant rotation speed and anon-pulse portion which corresponds to a reference position; a clockpulse generating circuit which generates pulses at equal intervals; acounter for counting the pulses of the clock signal from a reset valuewhen the angular signal changes from a first level to a second level; aprocessing circuit for providing a reference value by multiplying thecounted value of the counter when the angular signal changes from thefirst level to the second level and a constant that corresponds to thenon-pulse portion; and means, including a comparator, for generating adetection signal when the counted number of the counter becomes largerthan the reference value.
 6. The rotation position detecting device asclaimed in claim 5 further comprising: a latch circuit for latching thecounted value of the counter when the angular signal changes from thefirst level to the second level.
 7. The rotation position detectingdevice as claimed in claim 6 further comprising: a gate circuit whichmasks the detection signal outputted by the comparator as long as theprocessing circuit is calculating the reference value.
 8. The rotationposition detecting device as claimed in claim 5, wherein the angularsignal synchronizes with rotation of an internal combustion engine.